The present invention relates to a method of manufacturing a battery on which electrolyte layers are formed by coating electrolyte on electrodes and coating machines employed thereof.
Recently, portable electric equipment has been developed, hence, a battery has an important role as an electric source of such portable electric equipment. The portable electric equipment is required to be miniature and lightweight, in response to this request, the battery is also requested to be miniature in accord with accommodating space inside the portable electric equipment, and to be lightweight in order not to increase weight of the portable electric equipment as possible.
As the battery responding to such a request, in replace of a lead-acid battery and a nickel-cadmium battery, which used to be mainstream in the secondary battery, a lithium secondary battery and a lithium ion secondary battery whose energy density and output density are higher than that of these batteries are expected.
Conventionally, in the lithium secondary battery, or the lithium ion secondary battery, liquid-type electrolyte, which is dissolved lithium ion in nonaqueous solvents is employed as a material working for ion conduct (hereinafter, it is referred to as electrolyte liquid). With this reason, a package must be made of a metal case for preventing leakage and strictly maintain hermeticity inside the battery. However, with the metal case for the package, it is extremely difficult to produce a battery such as a sheet-like battery, which is thin and flat, a card-like battery, which is thin and small, or a battery, which is flexible and freer in shape.
In replace of the electrolyte liquid, it is therefore suggested that a secondary battery is employed such as gel-type electrolyte, which macromolecular compounds has electrolyte liquid including lithium salt, solid-type electrolyte in which lithium salt is diffused to macromolecular compounds having ion conductivity, or electrolyte in which a solid-type inorganic conductor has lithium salt. In these batteries, there is no leakage, so that the metal case is unnecessary as a package. Consequently, miniaturization reduction in weight and thickness in size of the battery by using a laminate film and the like as a package material are obtained to realize a battery freer in shape.
In case of using gel-type electrolyte, with a method described later, electrolyte layers are formed on electrode mixture layers formed on electrode collector. First, a belt-shaped electrode comprising a plurality of the electrode mixture layers intermittently formed on the belt-shaped electrode collector is impregnated in a tank accommodating electrolyte. Next, the belt-shaped electrode is pulled up from the tank and scraped the electrolyte adhering to both faces with a pair of scoops (doctor knives) in order to form the electrolyte layers having a predetermined thickness on the both faces of the belt-shaped electrode. After this, the belt-shaped electrode is cut into a plurality of electrodes between the electrode mixture layers, which are intermittently formed.
In the method of manufacturing the electrolyte layers like this, in case that any accidents happen, which stops the electrode from being conveyed, or decreases a speed at which the electrode is conveyed when the electrode is impregnated, a part of the electrode positioned in the tank when the accidents happen, absorbs the electrolyte than required, which causes a trouble to control an amount of the electrolyte. In this case, it requires that regions where the amount of the electrolyte increases are removed, however, a thickness of the electrolyte layers is almost the same between failure regions and normal regions, which requires control procedures such that the failure regions are marked every time when the accidents happen.
In case that the electrode mixture layers are formed on different regions in the surface and the back when forming the electrode mixture layers on the both faces of the electrode collector, a thickness of the electrode varies in part. Consequently, it is difficult to achieve the electrolyte having an even thickness by a method of scraping the electrode with the pair of scoops.
With a reason that the belt-shaped electrode comprising a plurality of the electrode mixture layers intermittently formed on the electrode collector is impregnated in the tank so as to form the electrolyte layers, the electrolyte directly adheres to the electrode collector on regions where the electrode mixture layers are not formed. In this case, when a lead, which becomes an electrode terminal, is attached to the regions on which the electrode mixture layers are not formed, a stripping electrolyte process is required.